The semiconductor industry, as well as unrelated industries, frequently hold and transfer thin planar objects in cassettes having a series of parallel, spaced apart horizontal slots which receive and hold a single planar object in each slot. Semiconductor wafers are frequently transferred from one processing station to another via cassettes. In some cases, cassettes are sized and shaped to hold film frames or other similar devices upon which a wafer has been mounted for processing and/or transporting.
Cassettes are used within the semiconductor industry primarily in processes which retrieve and process one wafer at a time. In particular, wafer cassettes are often used in conjunction with chemical mechanical planarization machines and in the packaging and assembly operations film frame cassettes are used in conjunction with sawing and die attach equipment. Wafers or the film frames upon which wafers have been mounted are typically loaded and unloaded from a cassette automatically by the processing equipment or a robotic mechanism. A robotic arm selectively retrieves the wafer or frame from the cassette, and transports the work pieces one at a time to a processing station. In the case of film frame cassettes, the frames are individually removed for processing, usually by an automated load/unload interface device on sawing or die attach equipment, and it is necessary that the frames be aligned and positioned in the correct location to avoid malfunction of the interface device.
The diameter of wafers has changed several times in recent years as larger wafers and processing equipment for larger diameter wafers has become available to the industry, and as the economics of larger diameter wafers has become evident. It is not uncommon for backend facilities, including packaging and assembly manufacturing to process wafers of more than one diameter, typically 150, 200, 250, and 300 mm. In order to hold the wafers and frames securely in place, each cassette is sized to accommodate a given wafer and/or film frame size. Therefore, the manufacturing facilities which store and transport wafers or wafers on film frames must store various frame and cassette sizes, and must make changes to the processing equipment or transport equipment for each different size wafer or frame. Typically, a cassette for each specific wafer size differs in width, height, depth, and other design features from a cassette for a different size wafer. The multiplicity of cassette sizes adds to storage space requirements, as well as inventory cost.
Modifications to automated equipment or equipment interfaces in order to facilitate different wafer and frame sizes result in costly work stoppages and increased cycle time. Equipment changes, particularly those involving mechanical modifications to interface mechanisms are labor intensive, time consuming, and are subject to set-up errors.
A significant problem associated with multiple cassette sizes requiring equipment set-up changes is the increased probability of improper alignment resulting in damage to costly wafers as a result of frames jamming into each other and sliding across the surface of a wafer.
Industries unrelated to semiconductors have similar issues with a multiplicity of cassette sizes; therefore, it would be an advantage not only to the semiconductor industry, but to unrelated industries as well, if a solution to the problems associated with cost of multiple cassette sizes, the equipment changes, and preparation required for handling multiple cassette sizes could be eliminated.